Data is stored on magnetic media by writing on the magnetic media using a write head. Magnetic media can be formed in any number of ways, such as tape, floppy diskette, and hard disk. Writing involves storing a data bit by utilizing magnetic flux to set the magnetic moment of a particular area on the magnetic media. The state of the magnetic moment is later read, using a read head, to retrieve the stored information. Data density is determined by the amount of data stored on an area of magnetic media and depends on how much area must be allocated to each bit. Data on magnetic media is often stored in a line or track. Magnetic media often have multiple tracks. In the case of disks, the tracks are nested annular rings with more bits per track and more tracks per disk with increasing data density. Data density or areal density, therefore, is determined by both the bit length and by the width of the bit. To decrease bit size, head size is decreased by fabricating thin film read and write heads.
Ongoing, important goals of researchers in magnetic recording technology include producing disk drive read heads that achieve strong signals, providing accurate readback of those signals, minimizing noise interference, and providing very high areal density while controlling manufacturing costs. Unfortunately, some of these goals directly conflict with one another. For example, to achieve ever-higher areal densities, track widths on a disk become smaller necessitating that the components used to read and write data also become smaller, which makes manufacturing more difficult and expensive.
High density recording, such as over 100 Gbit/in2, requires a highly sensitive read head. At higher densities, resistance changes in the head originating from the giant magnetoresistive (GMR) effect are reduced based on the progressively smaller dimensions of the length of the read head. The GMR effect (as well as the MR effect) is the measure of changes in electrical resistance of magnetically soft material, with the GMR effect found specifically in thin film materials systems. In current-in-plane (CIP) read heads, electrical current flows between contacts parallel to the disk or media surface through a GMR element or a read sensor with changes in resistance detected by voltage changes (i.e., readback voltage or output signal). More sensitive read heads, current-perpendicular-to-plane (CPP), have current flows through the films or GMR elements perpendicular to the long axis of the structure and parallel to the disk or media surface. The sensitivity of the CPP read heads has recently been further enhanced by building CPP read head structures that utilize tunneling magnetoresistance (TMR) concepts in which electrons “tunnel” through very thin insulators based on the magnetization of layers above and below the insulator.
In conventional current perpendicular-to-plane magnetic recording head design, the read sensor is shielded by both a bottom and a top shield as shown in FIG. 1A from an air bearing surface (ABS) view and a cross-sectional view in FIG. 1B. The top shield and the bottom shield are spaced apart on opposite sides of the reader stack in a longitudinal direction.
The read sensor reads back magnetic signals from written transitions. With increasing areal density, the ever shrinking written transitions require reader sensors with high read back amplitude. In conventional read sensor design, the sensed media field 200 decays exponentially along sensor stripe height direction, as shown in FIG. 2. The back end of the read sensor is not responsive magnetically.